1. Technical Field
This invention relates generally to printing machine-readable documents using magnetic toners, and more particularly to such printing wherein images having large solid areas are enhanced.
2. Background Art
The use of magnetic toner for creating magnetic image character recognition (MICR) such as used for bank checks is well known. U.S. Pat. No. 4,901,114 to Parker et al. discloses such a printer wherein magnetic toner is used to print those parts of the image that are necessary of the character recognition system, and non-magnetic, less expensive toner is used to print those remaining portions of the image.
Magnetic toner development stations generally have stringent specifications optimized for producing line images. Due to the magnetic attraction of magnetic toner to the magnets used in magnetic brush development stations, it is very difficult to develop large solid areas. This problem is compound because the relatively non-conductive magnetic toner tends to work its way between adjacent, conductive carrier particles, making the carrier chains non-conductive.
Although the Parker et al. patent discloses single-pass developent to print magnetic toner MICR images and non-magnetic toner images on the same document, that patent is concerned with printing different portions of the document with different toners; and not with using non-magnetic toner to fill in solid areas which are edged with magnetic toner.
3. Disclosure of Invention
Accordingly, it is a feature of the present invention to first develop a latent image with magnetic toner so that small details, line, and the edges of solids are developed; and to then develop the remaining undeveloped or underdeveloped portions of the latent image with non-magnetic toner to fill in the inside of the solid areas. Preferably, the magnetic toner development station has a development electrode spaced further from the photoconductor than the electrode of the non-magnetic toner development station.
The invention, and its objects and advantages, will become more apparent in the detailed description of the preferred embodiments presented below.